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Old 12-07-2011, 07:06 AM   #1
Ladowny
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Registered: Oct 2006
Distribution: Debian, OpenBSD
Posts: 19

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Encrypted LVM on a SAN with SSD fast cache drives failure


Hi

We have just purchased a new EMC SAN with SSD fast-cache ( http://www.emc.com/about/glossary/fast-cache.htm ).
I have set up a VM running database server with Postgres 8.4 on Debian squeeze 64bit with encrypted LVM partition and a second VM with unencrypted LVM, same spec otherwise. I was trying to determine how much impact the encryption will have on performance. The first results showed much slower performance of the encrypted one, but consecutive querries results were much better, encryption seemed to have minimal impact on the query speed.
The query used LIKE clause to search for records containing a string
Quote:
| Encrypted | Not encrypted
Selecting 78`786 records | 2 m 32s | 13s
Selecting 18`408`379 records | 13 s | 15s

total record count :30`016`693
I gathered this would be due to fast cache being used. During the second query the table was already moved to fast cache. However, when I was trying to run another query, updating a few milion records the encrypted server crashed. On VCenter I saw an alert "Alarm 'Virtual machine cpu usage' changed from Green to Yellow" and the machine threw some kernel panic messages on screen and froze. The other VM using unencrypted file system runs just fine.

The server was freshly installed with default debian settings, I just tuned Postgres a bit ( or maybe a lot, my databases are from 50 to 120 Gig each, so it would not run on default settings ).

Anyone have experience with running encrypted LVM on SAN with Fast-cache ? I'm a bit concerned with the result of my tests so far, don't want to store data on a server that's not reliable. Not sure what caused the issue, but it's kind of scary it happened.

Greg

Last edited by Ladowny; 12-07-2011 at 07:09 AM.
 
  


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